Combination lever ship&#39;s steering system

ABSTRACT

A compact combination lever ship&#39;&#39;s steering system is disclosed having unitary control features permitting ready selection of either of two preferred modes of operation. The ship&#39;&#39;s pilot may select lever operated proportional control of the ship&#39;&#39;s rudder steering engine with a direct display of rudder position for reference. The same combination lever control may be used for direct control of the ship&#39;&#39;s steering engine, rudder position again being displayed.

United States Patent [151 3,695,205

Thomas 51 Oct. 3, 1972 COMBINATION LEVER SHIP'S 2,796,576 6/1957 Braddonet al. ..318/588 STEERING SYSTEM 3,375,446 3/1968 Guyton ..338/198 [72]Inventor: tlvilliam G. Thomas, Charlottesville, Primary Examiner AndrewH Farrell Attorney-S. C. Yeaton [73] Assignee: Sperry Rand Corporation 8C 57 AB TRA T I22] Filed: Nov. 5, 1970 1 A compact combination leverships steering system is 1 PP N04 37,213 disclosed having unitarycontrol features permitting ready selection of either of two preferredmodes of operation. The ship's pilot may select lever operated [221 ES.((51. ..ll4ll44ll:33hlgls5ltii propo ion a1 control of the ship,s rudderSteering [58] Fntid 114/144 I gine with a direct display of rudderposition for 1 o reference. The same combination lever control may338/198 be used for direct control of the ships steering engine,

' rudder position again being displayed. [56] References Cited UNITEDSTATES PATENTS 7 Claims, 6 Drawing Figures 2,414,936 1/1947 Edwards etal. ..3l8/674 I l I |3ar v) 63 1 x64 54 5? 99 i I -60 POWER 1 SOURCE IRECTIFIERF I I00) 55 l i c 25b l 3 4 1 53 I 24 POWER AMPLIFIER 56 a9 92(as 66 /42r 67 POWER l SOURCE i 94 '6Bb 680 96 STEERING 97 w m l ENGINEPAIE'N'TEDums my 3.695.205

' snuaraurav J I l 22 I l E5 5% 281% INVENTOR.

BYv

ATTORNEY W/LL/AM' 6. 7/10/1445 PATENTEDncrs m sum 3 or 3' FIG. 6

i v INVENTOR. l V/LL/AM G. THOMAS ATTORNEY COMBINATION LEVER SHIP 'SSTEERING SYSTEM BACKGROUND OF THE INVENTION FIELD OF THE INVENTION Priorart ships steering systems have generally been of the type in which awheel or a lever controller has been used without follow up for controlof the ships steering engine. Turning the controller to the right or tothe left actuates the steering engine which moves the rudder in acorresponding direction until a limit stop is reached or until thecontroller is centered. The pilot may make judgments about the shipsresponse after its response is well established, but generally has nodirect or convenient means for determining with significant accuracy atthe time a turn is commanded what that response will ultimately be.

Other types of prior art steering systems provide proportional controlof the ships rudder with full follow up so that rudder response is moredirectly related to the magnitude of commanded turn. However, suchsystems are generally complex and, being complex, may suffer disablingfailures. Such systems generally do not lend themselves to readylocation of the point of failure. When failed, they may not provide asufficiently reliable degree of standby operation.

SUMMARY OF THE INVENTION A compact combination lever steering system forships is provided with a unitary lever controller permitting the shipspilot to select either of two modes of control of the ships ruddersteering engine. In a first control mode, the pilot may select leveroperated control of the ships steering engine and its rudder and mayobserve the turning performance of the ship in part by viewing a directdisplay of rudder angle as a reference. The display and the levercontroller are in close proximity so that lever command and rudderresponse are readily correlated. The combination lever controller may beused in a second mode, if desired, for direct control of the shipssteering engine without follow up. Rudder position is again displayed,the apparatus for proportional control being always on standby duty forinstant selection by the pilot.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of thecombination lever controller.

FIG. 2 is a top view of a portion of the controller of FIG. 1.

FIG. 3 is a cross section view of a portion of the apparatus of FIGS. 1and 2 FIG. 4 is a cross section view of the apparatus of FIGS. 1 and 2taken along the line 4-4 of FIG. 2.

FIG. 5 is a partial interior elevation view taken along the line 55 ofFIG. 4.

FIG. 6 is a diagram of the electrical circuits used in the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 presents a view of thelever steering actuator of the novel ships steering system as normallyseen by the pilot. A waterproof casing 1 is provided in which thesteering lever 2 is pivoted for angular motion, as

will be explained, and in which is also conveniently located azero-center electrical meter or indicator means 3 on which the pilot maycontinuously view a representation of rudder actual position relative toits null position whenever the steering system is operating. A cap 4 onthe half-circular housing 7 above the pivot shaft for lever 2 bears anindex marker 5 corresponding to the proper null position for lever 2. Araised marker 6 on top of the lever 2 adjacent the frontal portion ofcap 4 cooperates with index 5 to enable accurate nulling of lever 2.. Aswill be seen, the position of lever 2 is proportional to rudder orderwhen operating in the full follow up mode.

The upper face 8 of the portion of casing l in front of meter 3 supportsmetal blocks 9 and 9a symmetrically on either side of housing 7. As willbe seen, blocks 9 and 9a are provided with longitudinal bores foraccommodating respective spring-positioned pins 10 and 10a. Pin 10, whenimpacted by the vertical face 11 (not directly seen) of lever 2 acts asa first resilient mechanical stop. Likewise, pin 10a, when impacted bythe vertical face 11a of lever 2, acts as a second resilient mechanicalstop.

The structure of the apparatus of FIG. 1 may be more fully appreciatedby examination of FIGS. 2, 3, 4, and 5, wherein parts similar to thosein FIG. 1 are given the same reference numerals. In FIG. 2, it is seenthat cap 4 is fastened to the half-circular shell housing 7 by screws12, 12a, and 12b and that lever 2 extends under the cap 4 where it isfastened at its inner end to vertical shaft 13. FIGS. 2 and 3 show moreclearly the nature of the resilient mechanical stops comprising blocks 9and 9a. For instance, FIG. 3 shows block 9 and pin 10, block 9 beingprovided with a cylindrical cavity 14 for accommodating a stiff helicalwire spring 15. Pin 10 is provided with a head 16 slideable within bore14 and provides a first seat for spring 15. At its other end, spring 15abuts the inner face of a screw or other plug 17 fitted in a matingthreaded enlargement 18 of cavity 14. When the face 11 of lever 2 isforced against the rounded end 19 of pin 10, the latter is moved inwardalong its axis, carrying head 16 inward and compressing spring 15.

FIGS. 4 and 5 illustrate elements of the lever steering actuatorinternal of casing 1. Shaft 13 and its lower extension 13a are mountedfor angular movement in a bearing (not shown) within the central inwardprojection 20 of casing l. A gear 21 meshes with a second gear 22 onpotentiometershaft 23, potentiometer 24 having three electrical leads 25for purposes which will be explained. The potentiometer 24 is mountedwithin casing 1, being fixed to an inner wall of casing l by bolts 26,26a, and mount 28.

The lever shaft extension 13a drives a switch cam 27, seen more clearlyin FIG. 5, for operating switch 30 or switch 30a when lever 2 is movedto an extreme right or left position that depresses one of the pins 10,10a. Switches 30 and 30a are symmetrically mounted with respect to thenull position of lever 2 and therefore of switch cam 27 on base 280 byscrews 31, 31a, 32, 32a. Base 280 is, in turn, fixed to an inner wall ofcasing 1 by screws 29, 29a.

Switch 30 is provided with an actuator button 35 moved by arm 33 whenarm 33 is urged toward actuator button 35 by the rotation of arm 33about pivot 34.

Such rotation of arm 33 occurs when the face 37 of switch cam 27 impactsa roller 39 located at the button (35) end of arm 33. Impact of face 37on roller 39 and the consequent closing of switch 30 occur when the face1 l of steering lever 2 pushes stop pin into block 9 against spring 14.

In a similar manner, switch a, which is not seen in FIG. 4 for purposesof convenience, is provided with an actuator button a moved by arm 33awhen arm 33a is urged toward actuator button 35a by the rotation of arm33a about pivot 340. Motion of arm 33a occurs when the face 37a ofswitch cam 27 impacts roller 39a found on the button (32a) end of arm33a. Impact of face 37a and roller 39a and the consequent closing ofelectrical switching contacts within switch 30a occur when the face 11aof lever 2 pushes stop pin 10a into a block 9a against its associatedspring. When lever 2 is released, spring 15 or spring 15a will push itsassociated stop pin 10 or 100 outward, moving lever 2 and cam 27 back sothat both switches 30 and 30a are open. It is to be noted that theangularly separated switches 30 and 30 a are respectively equipped withelectrical leads 36 and 36a, whose purposes will become apparent. It isalso seen that casing 1 supports a dual position switch 40 whose controlhandle 41 is accessible outside of casing 1. Manual selector switch 40is provided with electrical leads 42 whose purpose will become apparent.

The apparatus shown in FIGS. 1 to 5 is employed by the ships pilot tocontrol the electrical servo and control system of FIG. 6 for operationof the ships rudder in one of two selectable modes. A first mode may betermed a proportional control mode with full follow up, rudder positionbeing fed back as a term used in the amplifier elements of the systemalong with commands inserted by moving the steering lever 2. Rudderposition is shown on meter 3. In a second selectable mode of operation,which may be referred to as the emergency mode, the amplifier elementsof the system are not used, but meter 3 is still caused faithfully toshow rudder position. The relative positions of lever 2 and meter 3permit the pilot at all times to judge the response of the ships rudderin relation to the position of the steering lever.

In FIG. 6, a conventional source 51 of alternating current power may beused to excite rectifier 52 and also to supply electrical energy to thesystem output power amplifier 53. The unidirectional voltage output fromrectifier 52 is supplied via electrical leads 54, 55 to potentiometerleads 25a, 25b, across the resistor 56 of potentiometric device 24. Thetap 57 of potentiometer 24 is driven by shaft 13a, as seen in FIG. 4, incommon with switch cam 27, and has its output lead 25c coupled as oneinput to power amplifier 53. The output of rectifier 52 is also suppliedthrough leads 54 and 55 and the respective leads 59 and 60 across aseries impedance circuit comprising substantially equal fixed resistors63 and 64.

In addition, the unidirectional voltage output of rectifier 52 issupplied through leads 54 and 55 and the respective leads 61 and 62across the resistor 66 of potentiometer 65. Potentiometric device has anangularly movable tap 67 driven by the shaft 68b in synchronism with theinstantaneous position of rudder 50. Tap 67 is coupled by lead 69 as asecond input to power amplifier 53.

Power amplifier 53 may take any of several forms, including knownsemiconductor or vacuum tube power amplifiers or magnetic amplifiers ofthe general type disclosed in the DeWestfelt U.S. Pat. No. 2,813,236,entitled Control System for Electrical Servomotors, issued Nov. 12,1957, and assigned to the Sperry Rand Corporation. The application ofsuch amplifiers in ships steering controls is further discussed invarious sources such as the Braddon et al. U.S. Pat. No. 2,796,576entitled Maneuverable Automatic Pilot for Ships, issued June 18, 1957,and also assigned to the Sperry Rand Corporation.

The output of a device suitable for use as power amplifier 53 willconventionally appear on a set of four electrical leads 70a, 70b, 70c,and 70d. Leads 70a and 70b are connected across coil of differential orpower relay 82, while leads 70c and 70d are coupled across coil 81thereof. Relay 82 includes an armature 83 movable about pivot 84according to the respective excitation of coils 80, 81 for connectingleads 42a and 42b through contact 85 or for connecting leads 42b, and420 through contact 86. Relay 82 is a power switching device oftenemployed for the control of ships steering engines, such as engine 95.It will be apparent that contact 85 is made when one sense of turn isdesired, while contact 86 is made if an opposite sense of turn iscommanded, as is further explained in the aforementioned Braddon et al.U.S. Pat. N 0. 2,796,576.

In the above desired arrangement for the first mode of operation of thesteering system, the manual selector switch 40, first introduced in FIG.4, will not be in the position shown in FIG. 6, but manual linkage 93operated by handle 41 will cause blades 90, 91, and 92 respectively tocontact the terminals 87, 88, and 89 of the respective leads 42a, 42b,42c, electrical leads also seen in FIG. 4. Switch blades 90 and 92 arerespectively connected by leads 42d, 42f across the activating coils 96,97 of rudder steering engine or motor 95. Coils 96, 97 may representcoils of an electrical motor, or may be the control solenoids which, forinstance, move the four-way sensitive control value of a hydraulic servomotor of conventional nature. Switch blade 91 is connected by lead 42ethrough power source 51a and lead 94 to the center tap 98 betweensteering engine coils 96 and 97. Power source 51a may by any convenientsource of alternating power; sources 51 and 51a may in practice beidentical. Depending upon the contacted status of terminals 85 and 86,the ship s rudder steering engine or motor causes rudder 50 to be driventhrough shaft 68a in one rotational sense or the other.

It is thus seen that the dual bridge circuit comprising potentiometricdevices 24 and 65 and their associated circuits provides control signalsto power amplifier 53 for operation of relay 82 and consequently for thecontrol of steering engine 95 and rudder 50. The second bridge circuitinvolving rudder potentiometer 65 and the fixed resistors 63 and 64 alsohas a role to play during operation of the system in the first mode. Itis seen, for example, that meter 3 is connected between lead 69, andtherefore the movable tap 67 of potentiometer 65, and the mid-pointterminal 99 between resistors 63 and 64. Since resistors 63 and 64 havefixed values, unbalance of the associated bridge by motion ofpotentiometer (65) tap 66 causes the pointer of meter 3 to move insynchronism with the movement of rudder 50. Meter 3 will preferably be ataut band suspension zerocenter microammeter whose calibration may beeffected by positioning tap 100 of a shunting potentiometer 101 placedacross meter 3. The deflection of meter 3 is observed in terms of theposition of steering lever 2, affording a ready understanding of thebehavior of the system at all times. I

In the second mode of operation, the handle 41 of switch 40 of FIG. 4 ismoved to position the switch blades 90, 91, and 92 as actuallyillustrated in FIG. 6. In this instance, switch cam 27 and switches 30and 30a of FIGS. 4 and 5 come into play, along with leads 42g, 42k, and42i since switch blades 90, 91, and 92 now contact the respectiveterminals of leads 42g, 42h, and 42i. With lever 2 and therefore switchcam 27 approximately centered, the angularly separated on-off switches30 and 30a are normally open, being held open, for example, by springs71 and 72. When lever 2 is moved to its extreme position to engage andmove one resilient mechanical stop pin, switch 30 contacts the terminalof lead 36. In this instance, a circuit path is completed along lead42g, through blade90 of switch 40, through lead 42d, coil 96 of steeringengine 95, lead 94, power source 5111, lead 42e, blade 91 of switch 40,and the common lead 42h back to switch 30.

Should the opposite turn command be desired, lever 2 is moved to depressthe opposite resilient mechanical pin and on-off switch 30a contacts theterminal of lead 36a. As a consequence, a circuit path is completedalong lead 42i, through blade 92 of switch 40, through lead 42f, coil 97of steering engine 95, lead 94, power source 51a, lead 42e, blade 91 ofswitch 40, and the common lead 42h back to switch 36a.

While the bridge circuit associated with potentiometers 24 and 65 isactive in the second mode of operation and continues to supply signalsto power amplifier 53, such is done on a standby basis. Thus, the outputof amplifier 53 is instantaneously available to the pilot by operationof selector switch 40. It will be understood that other choices for thelocation of manual selector switch 40 may be made, such as a location onlever 2 where it may be used to control a remote relay to move selectorswitch 40. In any event, the bridge circuit associated with fixedresistors 63 and 64 and rudder potentiometer 65 is enabled to continueto supply rudder position indications on zero-center display 3.

In operation of the system, it is seen that the ships pilot is givenfreedom of choice to operate the steering system in the mode he deemsmost suited to use in the particular circumstances in which he finds hisship. When operating in the first mode, full follow up electricalcontrol is exercised over rudder 50. Since there is no mechanicalconnection between the lever 2 and the steering engine 95, lever 2 maybe positioned with no substantial effort and the rudder 50 will respondto any such movement of lever 2 and may be positioned accurately andquickly at any angle between its two hardover extremes. When operatingin the first mode, hardover motion of lever 2, even when sufiicient toactuate one or the other of the angularly separated resilient stop pinsor 10a, does not cause the cam switch 27 to produce any disturbingaction even if switch 36 or switch 36a is closed. In addition to usingthe benefits inherent in proportional control in the first mode, the

ship's pilot has access by virtue of meter 3 to information on themomentary behavior of the rudder 50 and is thus able readily todetermine the performance of the control and to detect failure of followup.

Operation in the second mode is available not only for emergency use,but may be preferred by some pilots for use under special circumstances.It will be appreciated that there is less equipment involved inoperation in the second mode and that reliability may therefore beinherently greater. Being highly reliable, the second mode apparatus isan effective standby for the majority of pilots which prefer to useproportional control. Operation in the non-follow up mode permits theships rudder to move only when lever 2 is held against a stop pin 10 or10a and rudder movement immediately stops when lever 2 is released.

The versatility of the novel ships steering system is further seen byconsideration of its self-testing qualities. If a failure occurs whenoperating in the first mode, the pilot can to a substantial degreedetermine the locus of the failure by moving manual selector switch 40to its second mode position. If meter 3 remains operative in the modetwo condition, there is power present within the bridge circuits andtherefore probably no failure of those circuits or of the power supply51 or rectifier 52. The indication is failure of power supply 51a or ofrelay 82. However, if meter 3 does not produce a following indicationwith the system in the second mode of operation, the problem is probablyseated in power supply 51, in rectifier 52, in the bridge circuits, orin the power amplifier 53. The steering engine 50 may itself havefailed, indicating the need to shift to use of a standby steeringengine.

For the ships pilot preferring to use the direct control featured in thesecond mode of operation when in close or dangerous situations in whichthe thought of a possible failure in an electrical control circuit isabhorrent to him, mode two operation may be selected. The pilot is stillbenefitted, as he was in mode one operation, by the presence of rudderposition information on meter 3. Lengthy navigation in the second modeis entirely feasible; in fact, the ship may readily be sailed to homeport using the direct control of mode two operation after a failure of amode one component, where the latter may be more readily repaired orreplaced than at a foreign port.

In addition to the simplicity, versatility, and low cost features of thenovel control system, it is seen that it readily accommodates additionof other features which are at times found desirable in ships steeringsystems. For example, addition of a gyrocompass navigation system isfeasible, as well as of means permitting control of the gain of thesystem according to different loading and speed conditions, or of aweather adjustment circuit, or of other adjustments of the type referredto in the aforementioned Braddon et al. US. Pat. No. 2,796,576, in theWest US. Pat No. 2,719,502, entitled: Automatic Pilot for Ships, filedOct. 4, 1955, and assigned to the Sperry Rand Corporation, andelsewhere.

While the invention has been described in its preferred embodiments, itis to be understood that the words which have been used are words ofdescription rather than of limitation, and that changes within thepurview of the appended claims may be made without departing from thetrue scope and spirit of the invention in its broader aspects.

1 claim:

1. Apparatus for operation of a rudder steering motor comprising:

steering lever means movable to the right or left about an axis andbetween fixed angularly separated extreme positions,

first and second electrical circuit means controllable by said levermeans, and

manual selector means for applying electrical power to said ruddersteering motor selectively through at least a portion of said first orsecond electrical circuit means,

said first electrical circuit means comprising bridge means unbalancedby motion of said lever means or said rudder steering motor andsupplying an electrical output for determining operation of said ruddersteering motor,

said second electrical circuit means comprising switch means closable atsaid extreme positions of said lever means for supplying an electricaloutput for determining operation of said rudder steering motor.

2. Apparatus as described in claim 1 comprising:

fixed impedance means connected across said bridge means, and

indicator means connected to said bridge means and to said fixedimpedance means for displaying the instantaneous position of said rudderindependent of the selected state of said manual selector means.

3. Apparatus as described in claim 1 wherein said bridge meanscomprises:

first and second potentiometric means having respective first and secondmovable pick off means,

said first pick off means being movable by said steering lever means,

said second pick off means being movable by said rudder steering motor,

said first and second pick off means being adapted for the supply of anelectrical output for determining operation of said rudder steeringmotor, and

power supply means connected across said potentiometric means.

4. Apparatus as described in claim 3 wherein said first and second pickoff means supply an electrical output for the differential control ofdifferential relay means for determining operation of said ruddersteering motor.

5. Apparatus as described in claim 1 wherein said second electricalcircuit means comprises:

first and second switch means symmetrically located respectively at saidfirst and second angularly separated extreme positions, and

cam means positioned by said lever means for actuating said first switchmeans only at said first extreme position or said second switch meansonly at said second extreme position.

6. Apparatus for operation of a ships rudder steering motor comprising:

a casing, lever means movable to the right or left about an axis tween agularly separated extreme ositions, sh means or rotatab y supporting sailever means relative to said casing on said axis and extending into theinterior of said casing.

potentiometric means within said casing driven synchronously with saidshaft means adapted for generating proportional electrical signalsrepresenting lever position for selectively controlling said steeringmotor,

on-off switch means located at said angularly separated extremepositions of said lever means adapted for generating on-ofl' controlsignals in response to the location of said lever means with respect tosaid extreme positions for selectively controlling said steering motor,and

means for selecting said proportional or said on-off signals for controlof said steering motor.

7. Apparatus for operation of a rudder steering motor comprising:

a casing,

lever means movable to the right or left about an axis between fixedangularly separated extreme positions,

shaft means for rotatably supporting said lever means relative to saidcasing on said axis and extending into the interior of said casing,

potentiometric means within said casing driven synchronously with saidshaft means adapted for generating proportional electrical signalsrepresenting lever position for selectively controlling said steeringmotor,

on-off switch means located at said angularly separated extremepositions of said lever means adapted for generating on-off controlsignals in response to the location of said lever means with respect tosaid extreme positions for selectively controlling said steering motor,

resilient mechanical stop means activated by motion of said lever meansin a range of positions of said lever means including the angularpositions at which said on-off switch means is operated, and

separate switch means for selecting said proportional or said on-offsignals for control of said steering motor.

1. Apparatus for operation of a rudder steering motor comprising:steering lever means movable to the right or left about an axis andbetween fixed angularly separated extreme positions, first and secondelectrical circuit means controllable by said lever means, and manualselector means for applying electrical power to said rudder steeringmotor selectively through at least a portion of said first or secondelectrical circuit means, said first electrical circuit means comprisingbridge means unbalanced by motion of said lever means or said ruddersteering motor and supplying an electrical output for determiningoperation of said rudder steering motor, said second electrical circuitmeans comprising switch means closable at said extreme positions of saidlever means for supplying an electrical output for determining operationof said rudder steering motor.
 2. Apparatus as described in claim 1comprising: fixed impedance means connected across said bridge means,and indicator means connected to said bridge means and to said fixedimpedance means for displaying the instantaneous position of said rudderindependent of the selected state of said manual selector means. 3.Apparatus as described in claim 1 wherein said bridge means comprises:first and second potentiometric means having respective first and secondmovable pick off means, said first pick off means being movable by saidsteering lever means, said second pick off means being movable by saidrudder steering motor, said first and second pick off means beingadapted for the supply of an electrical output for determining operationof said rudder steering motor, and power supply means connected acrosssaid potentiometric means.
 4. Apparatus as described in claim 3 whereinsaid first and second pick off means supply an electrical output for thedifferential control of differential relay means for determiningoperation of said rudder steering motor.
 5. Apparatus as described inclaim 1 wherein said second electrical circuit means comprises: firstand second switch means symmetrically located respectively at said firstand second angularly separated extreme positions, and cam meanspositioned by said lever means for actuating said first switch meansoNly at said first extreme position or said second switch means only atsaid second extreme position.
 6. Apparatus for operation of a ship''srudder steering motor comprising: a casing, lever means movable to theright or left about an axis between angularly separated extremepositions, shaft means for rotatably supporting said lever meansrelative to said casing on said axis and extending into the interior ofsaid casing. potentiometric means within said casing drivensynchronously with said shaft means adapted for generating proportionalelectrical signals representing lever position for selectivelycontrolling said steering motor, on-off switch means located at saidangularly separated extreme positions of said lever means adapted forgenerating on-off control signals in response to the location of saidlever means with respect to said extreme positions for selectivelycontrolling said steering motor, and means for selecting saidproportional or said on-off signals for control of said steering motor.7. Apparatus for operation of a rudder steering motor comprising: acasing, lever means movable to the right or left about an axis betweenfixed angularly separated extreme positions, shaft means for rotatablysupporting said lever means relative to said casing on said axis andextending into the interior of said casing, potentiometric means withinsaid casing driven synchronously with said shaft means adapted forgenerating proportional electrical signals representing lever positionfor selectively controlling said steering motor, on-off switch meanslocated at said angularly separated extreme positions of said levermeans adapted for generating on-off control signals in response to thelocation of said lever means with respect to said extreme positions forselectively controlling said steering motor, resilient mechanical stopmeans activated by motion of said lever means in a range of positions ofsaid lever means including the angular positions at which said on-offswitch means is operated, and separate switch means for selecting saidproportional or said on-off signals for control of said steering motor.